System and method for thermophilic anaerobic digester process

ABSTRACT

An anaerobic digestion system is provided that includes a blend tank operable to control and perform pre-treatment of feedstock. An anaerobic digester is operable to digest the feedstock provided from the blend tank in a totally enclosed oxygen-free environment within a specific temperature range. A bio-mass tank processes liquid digestate from the anaerobic digester. One or more baffles are positioned in the digester, with the one or more baffles providing for plug flow through at least a portion of the digester to create baffled zones that are at least partially operable independently of adjacent baffled zones. A bio-mass tank processes liquid digestate from the anaerobic digester. An energy source is coupled to the anaerobic digester.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.14/036,747 filed Sep. 25, 2013, which is a continuation-in-part of U.S.application Ser. No. 13/598,188 filed Aug. 29, 2012, all of whichapplications are fully incorporated herein by reference.

BACKGROUND

The primary anaerobic digester processes on the market, that areavailable for industry/agriculture/municipal waste treatment andenvironmental remediation, include digesters which are either in groundor above ground. In addition, they operate generally at thepsychrophilic or mesophilic temperature ranges; however, there are somethermophilic units in operation. The psychrophilic units operatenormally at a temperature of 18° C. (65° F.) and the mesophilic units ata temperature range of 35° C. to 40.5° C. (95° F. to 105° F.). There aremany variations with these designed anaerobic systems, and each hascertain advantages. Detailed below are general descriptions of the threemajor classes of digester with a further explanation as to some of theircritical limitations.

The least expensive digester is an in ground system, such as a lagoon,which is generally an excavated shallow basin with a very large surfacearea. The sidewalls can be earthen and may include flexible membranecovers. There is generally no agitation in these units and most operateat ambient temperature, i.e.—psychrophilic. In-ground systems (i.e.lagoons) have certain intrinsic problems such as dilution of the processfrom either groundwater beneath the lagoon or rainwater from the sidesor top. Rainwater and snow/ice that accumulates on the flexible membranecover will depress the cover in certain areas and cause the biogas tocollect in pockets. Unintended water within the process dilutes theorganic matter, and disrupts the digester temperatures within the unit,affecting the performance and efficiency. High winds and UV radiationalso cause problems, damaging the flexible covering. Given the geometryof these lagoons, which are relatively shallow with a large surfacearea, evaporation combined with the lack of uniform agitation, causes asignificant and inevitable accumulation of inorganic and heavy organicmatter. Generally, these systems are shut down annually for over a monthto allow for solids removal and subsequent restart of the process.Maintaining proper operating temperature is recognized as a technicalproblem endemic to these units. This lack of temperature and exposuretime results in a marginal and unpredictable pathogen kill. Most if notall in ground lagoons require a secondary lagoon in which the processedfeedstock needs up to an additional 180 days to complete the process tomeet nutrient management requirements. Additional aerobic composting inwindrows may also be required.

Some in-ground units may incorporate concrete channels, which are laidout in either a long linear fashion or are in a U-shaped configuration.These units typically have concrete walls with concrete lids (orflexible membrane covers) and are built into the ground to retainprocess heat. These units are generally mesophilic. Heating is typicallyprovided by heating coils or pipes installed either under the digesterconcrete channel or in the central concrete wall, which separates thetwo adjacent channels of the U-shaped configuration. In all cases, theheat is transferred by a combination of conduction and convectionthrough the wall and then across the full width of the plug flow withinthe channel. The hydraulic residence time (HRT), which is the durationfor which material to be digested will remain in the digester, rangesfrom 18 to 28 days. This long duration time necessitates a long digesterchamber length and/or a slow throughput which in turn introducesmechanical difficulty providing proper and uniform agitation along thefull length of the digester. As a result, without consistent agitation,heating is not uniform and hot and cold areas develop along the lengthof the digester. Negatively impacting digester performance as measuredby throughput, volatile solids destruction, methane gas production andpathogen kill rates. In addition, the lack of uniform agitation alongthe length of the digester results in the accumulation of inorganic andheavy organic materials that have been introduced into the digester. Itshould be noted that although the heavy organic matter can be brokendown within the digester, any overlay of inorganic matter above theheavy organic matter (such as sand) may isolate the organic matter fromthe anaerobes. Over time, and generally within one year, the digesterneeds to be shut down to remove this accumulation of material. This isnecessary as the digester's operating volume slowly decreases, due tothis buildup, which, if left unattended, will ultimately blind off andrestrict the flow through the digester. When this type of digester isshut down, cleaned out and restarted, up to a month of operating time isgenerally lost.

The above ground, anaerobic digester systems are normally made of pouredin place concrete or steel construction materials and insulated asrequired. These materials are sturdy and water tight thus eliminatingmany of the intrinsic problems associated with lagoons such as water andwind. However, heat management is very critical to the efficientperformance of this type digester. Generally, these vessels arecylindrical in nature and are approximately 12 m (40 ft.) in diameter,and 12 m to 15.25 m (40 to 50 ft.) in height with a vessel volume of2500 m³ (88,290 fP) and greater. In the case of the mesophilic unitsresearched, hot water piping is usually located around the interiorcircumference of the vessel used as an aid in maintaining the optimaloperating temperature. An efficient digester should have uniformtemperatures throughout the vessel, within a tight tolerance of +/−1.2°c. or 2° F. However, convective and conductive heat transfer alone donot provide for homogenous heating throughout a vessel of this size.Therefore, in order to move heat to the center of the vessel mass,agitation is required. This is normally provided by a top or sidemounted unit with blades and sufficient energy to occasionally roll overthe vessel contents. Top mounted agitators are usually located offcentre with horizontal paddles near the top and bottom of the shaft.These agitators attempt to distribute the heat and achieve more uniformtemperatures within the digester; however the flow related processrequirements for the digester are compromised. The fresh feedstock ismixed in with the older feedstock very quickly, negatively impactingvolatile solids destruction, methane gas production, yield, and pathogenkill.

In addition to these above ground anaerobic mesophilic digester systems,there are similar units (far fewer) operating at the thermophilictemperature range of 44° C. to 70° C. (11° F. to 160° F.). Heatmanagement is even more critical to the efficient performance of thistype of digester. Generally, as in the case of the mesophilic type ofdigester described above, these thermophilic units have similardimensions, capacities and heating/agitation systems. Due to the higheroperating temperature of these other thermophilic units, the quantityand resulting surface area of the hot water piping located around theinterior circumference of the vessel is increased. To attain the tighttemperature tolerances required for digester efficiency, external heatexchangers may be required as convection and conduction alone may notsuffice. The temperature of the hot water must also be increased toaccelerate the heat transfer rate. This increased b.T then leads tolocalized caking and subsequent insulation of the heating pipes. Theintensity or level of agitation must also be increased to aid in theheat transfer and the required tight temperature control demanded by thethermophilic process. This increased agitation has the side effect ofcausing the methane producing bacteria to become dormant and produceless gas. The flows of the contents through the vessel as a result ofthe increased agitation will also short circuit the passage of thefeedstock through the unit, compromising pathogen kill certainty. Thisshort circuit condition does not permit the feedstock to be held at thehigher system operating temperatures for the length of time mandated toachieve pathogen kill levels.

Consequently, many of the systems in use as described above require asecondary vessel to finish the digestion process, adding to theHydraulic Retention Time (HRT). In the event that a secondary anaerobicdigester is not installed, the discharge from these digesters can bedewatered and transferred to storage areas for wind rowing. Wind rowing,which is aerobic digestion, is used to complete the overall digestionprocess to meet nutrient management requirements. Each incrementalprocess step adds significantly to the overall digestion time duration,as well as project cost, operational cost, and overall arearequirements. If these additional process steps are not included, thedigester performance (as measured by methane gas production, quality,volatile solids destruction, pathogen kill, hydraulic residence time andthe final digestate chemical inertness), will be measurably less thanthe results from the digester technology as covered by this patentdescription.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent upon a reading ofthe specification and a study of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a side view of an example of a thermophilic anaerobicdigester.

FIG. 2 depicts a cross sectional view of the example of the digesteralong section line A-A shown in FIG. 1.

FIG. 3 depicts the structure of an example of an agitator for thethermophilic anaerobic digester shown in FIGS. 1-2.

FIG. 4 depicts an example of a process flow diagram of an anaerobicdigestion system utilizing the thermophilic anaerobic digester shown inFIGS. 1-2.

FIG. 5(a)-(e) depicts a cross-section of the digester.

FIG. 6 illustrates one embodiment of a location of a sectional viewalong section line F-F of the anaerobic process as shown in FIG. 4

FIG. 7 illustrates a cross sectional view of an example of the microwaveorganic material heating loop in parallel with the steam heatingexchanger at the blend tank.

FIG. 8 illustrates an example of an in pipe microwave heating unit.

DETAILED DESCRIPTION

The approach is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” or “some” embodiment(s) in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

A new approach is proposed that contemplates systems and methods tosupport an environmentally-friendly, “green” thermophilic anaerobicdigestion system. The system includes a thermophilic anaerobic digesteras well as various independent modular anaerobic units to generatebio-methane from certain organic energy sources, including but notlimited to, among other things, green municipal waste, restaurant andorganic waste and effluents from industries such as breweries, grocerystores, food processing plants, granaries, wineries, pulp and papermills, ethanol and biodiesel plants, fat and animal rendering,agricultural field crops, organic sludge accumulation within lagoons andwaterways, marine organic matter and animal manure. The thermophilicanaerobic digestion system is uniquely designed to handle many types ofindustrial and municipal organic waste streams simultaneously orseparately. It also offers advantages over current digester systems,including its more modular and inter-changeable design (which expeditesproject construction), faster throughput digestion, smaller spacerequirements, higher gas production, superior pathogen and BOD/CODdestruction rates, better odor capture and control, higher flexibilityof feedstock usage.

The thermophilic anaerobic digestion system is primarily aimed at theeffect of inorganic matter on system. An anaerobic digester modular unithas been designed for experimental purposes and information gained fromthe design, installation, testing, operational monitoring and recordingof the unit has been accumulated, verified and incorporated herein.Among those operational findings it is discovered that, regardless ofthe separating pretreatment used, inorganics, if originally in thefeedstock cannot be completely removed. Thus one of the novelcharacteristics of this system is its self-cleaning attribute, whichenables the system to continuously operate using a contaminatedfeedstock. Additionally, other design attributes provide for ease ofoperation. The presence of wood shavings as a bedding material, foundfrequently in agricultural manure, does at times plug associated processpipelines of diameters 3 inches and smaller. This is remedied byinstallation of water lines where outlets are attached in strategiclocations with valves for back flushing for both above ground and inground lines.

FIG. 1 depicts a side view of an example of a thermophilic anaerobicdigester 100 utilized by the anaerobic digestion system. Although thediagrams depict components as functionally separate, such depiction ismerely for illustrative purposes. It will be apparent that thecomponents portrayed in this figure can be arbitrarily combined ordivided into components. FIG. 2 depicts a cross sectional view of theexample of the digester along section line A-A shown in FIG. 1.

The thermophilic anaerobic digester 100 depicted in FIGS. 1 and 2includes a cylindrical digester vessel (tank) 42 mounted horizontallyabove ground and optimally sloped between 1° to 5° off horizontal,although other angles will function but at reduced efficiency. Thevessel 42 can be fabricated from carbon steel and when closed off issealed to oxygen from the atmosphere providing for the anaerobicenvironment. The vessel 42 is supported by vessel saddle supports 44.These supports 44 raise the tank off the ground there by permitting theinstallation of digester heating device 52 and related equipmentinsulating layer 128. This vessel design was selected to maximizehydraulic plug flow characteristics and integrity. Plug flow exists wheneach batch of new feedstock travels the length of the digester vessel 42without intimate mixing with the feedstock batches added eitherbeforehand or after that particular batch. The slope of the vessel 42causes the heavier material, which tends to settle to the bottom of thecylindrical vessel 42, and has a higher concentration of inorganics totravel with the plug flow from the in-feed end to the discharge end. Thevessel design/orientation also facilitates the installation of digestervessel internal baffle(s) 40 and variable decanting at the discharge ofthe thermophilic anaerobic digester 100. These baffles as depicted inFIGS. 1, 2, 3 and 5 and identified as 40 are mounted to the centralshaft of the agitator identified as 32 and located between the agitatorpaddles, identified as 36 and specifically shown in FIGS. 1, 3 and 5.Baffles can be installed at some or all of the locations as depicted inFIG. 3. These baffles 40 are mounted to the shaft and are thereforeinstalled when the agitator is inserted into the digester vessel 42FIG. 1. Note that the central baffle, as depicted in FIG. 5, section C-Calthough also mounted to the shaft 32, is fabricated with a perimetersection that will ride in a corresponding non-wear internal saddlearrangement to support the central portion of the agitator that runs thefull length of the digester. In various embodiments, the baffles canhave tree functions depending on where they are located. FIGS. 1 and 3show the baffles located between the sections of the agitator radialpaddles located along the agitator shaft. The FIGS show up to threebaffles which can provide up to five discreet zones in the digester.These internal baffles 40 ensure that the plug flow traveling throughthe thermophilic anaerobic digester 100 must follow a predetermined pathwhich in turn ensures no intermixing. With these separate zones thezones can be operated with different operating conditions includingtemperatures to achieve both mesophilic and thermophilic digestionzones. The baffles will ensure true plug flow as the material in onezone must flow through the narrow convergence between the outer diameterof the baffle and the inner diameter of the digester before flowing intothe next digestion zone.

In addition, the baffles limit the material within the digester to avery narrow flow path which makes it possible to get a veryrepresentative pH measurement of the material in this area. Byinstalling sample/chemical injection valves at these specific locations,it is possible to measure and control the pH within the various digesterzones.

As the baffles are installed along the overall agitator shaft lengthprior to installation, it is possible to not only decide if baffles willbe positioned at certain locations, but whether or not full diameter orpartial diameter baffle needs to be installed. The central baffleposition also acts as a support in the center of the agitator, therebyreducing the cross-section for the agitator shaft assembly and thesubsequent fabrication cost. These process attributes optimize HydraulicRetention Time, Solids Retention Time, upstream inoculation, downstreamsolids separation and pathogen kill.

In some embodiments, the dimensions of the digester vessel 42 providefor a modular system that can be transported by rail or road to theinstallation site. This transportation flexibility allows thethermophilic anaerobic digester 100 depicted in FIGS. 1 and 2 to be usedfor a variety of process applications such as the one shown in FIG. 4.In addition, the digester vessel 42 can be fabricated off-site more costeffectively in fabrication shops thereby enhancing quality, productionschedules and unit costs. Also, this modular concept (which permits fullsize digester vessel 42 shipping to site) also permits the costeffective addition of incremental modules such as thermophilic anaerobicdigester 100, which in turn allows allocation of different feedstocks todifferent units on the same site. The modularity and limited foot printpermit installations at existing sites which have been judged to be landlocked and too small for an anaerobic digester installation using othertechnologies.

One of the key distinctions of the thermophilic anaerobic digester 100depicted in FIGS. 1 and 2 that sets it aside from these otherthermophilic units currently available is the totally different vesseldimensions, modularity of capacity additions, heating and contentsagitation as well as the pretreatment feedstock conditioning. The onlyfeature they share is the operating temperature. Since the vesselgeometry of a length to diameter ratio is set to 3:1 to 5:1 to optimizethermophile and feedstock mixing through the use of a longitudinalagitation arrangement (co-axial with the horizontal digester vessel 42),there are no “unmixed” areas of the thermophilic anaerobic digester 100.This optimized mixing configuration, combined with the sloping vesselconfiguration, moves heavy organic and inorganic materials (whichaccumulate in the rounded “belly” of the digester 100) and slowlypropels this accumulated material to the discharge end. Consequently, noaccumulations build up and therefore, shutdowns due to plugging or lossof operating capacity do not occur. Therefore the thermophilic anaerobicdigester 100 is a self-cleaning unit and very tolerant of a contaminatedfeedstock. These unique features of the thermophilic anaerobic digester100 and process allow the digestion of less uniformly sized feedstock.There are no negative implications to feeding the anaerobic digester 100with feedstock organic matter up to 2 em (0.75 in) in diameter.

In some embodiments, the digester heating system 52 and 170 are externalto the digester vessel 42. The vessel 42 is fabricated with a waterjacket along the underbelly of the vessel 42, utilizing convection andconduction heat transfer for homogenous heating throughout the vessel42. There is no potential for contamination of the vessel contents dueto leakage of any re-circulated glycol or other heating solutionsincluding but not limited to, saturated steam or hot water.

Alternatively, a thermal electric blanket can be used for each digesterzone, which has electrical heating elements embedded into it and thenattached that with mastic to the outside of the digester in theappropriate locations, and controlled by thermostat. This is a lesscostly alternative, and does not require either a steam or hot waterboiler.

Another embodiment uses using infrared or microwave to indirectly heatthe digestate as well as a cross flow heat exchanger at the blend tankto remove heat from the digestate removed from the digester which is notused to inoculate new feed stock going into the blend tank. Thetransferred heat would then preheat the manew material going into theblend tank.

In some embodiments, the thermophilic anaerobic digester 100 depicted inFIGS. 1 and 2 requires a Hydraulic Retention Time (HRT) of 3 to 7 daysas compared to an average of 16 to 80 days for psychrophilic, mesophilicor other forms of thermophilic anaerobic digesters. Completion ofdigestion is achieved when the percentage volatile solids destructionplateaus and longer residence time does not significantly increase thelevel of volatile solids destruction. Other digesters may define HRTbased upon this criterion or simply based upon digester residence time.This latter approach doesn't incorporate any final Volatile solidsdestruction targets. Consequently, gas production may not be optimized.If the process must comply with government nutrient management criteria(application of digestate to open land) the volatile solids destructionlevels are too low and ammonia content may be excessive. In such casesadditional digestion process steps may be required.

In some embodiments, the thermophilic anaerobic digester 100 depicted inFIGS. 1 and 2 can achieve volatile solids destruction (VSD) levels of50% to 65% for animal waste. The best VSD's achieved by these othertechnologies will be up to 53%, with averages in the low to mid 40's.The FDA has defined that a certain temperature/duration is required inorder to achieve effective pathogen kill. Although some current digestertechnologies are operated for more than the extended time periodsrequired by the appropriate government agency, their low temperaturesare insufficient to achieve the pathogen kill required to achievecompliance with governmental regulatory mandates concerning nutrientmanagement. In fact, all mesophilic systems need to sanitize certainfeedstocks (or the digestate) for 1 hr. at 70° C. (160° F.) in order toachieve compliance. One of the advantages of the thermophilic anaerobicdigester 100 and its thermophilic process is that most pathogens arekilled during the initial 24 hours of operation. Current regulations(both European and North American) state that 20 hours at 55° C. (130°F.) is sufficient. Subsequently, after a normal HRT duration, thepathogen kill using the thermophilic anaerobic digester 100 is 99.999%.

Solids Retention Time (SRT) is the most significant variable, whichindicates the amount of solids conversion (Volatile Solids (VS)) tobiogas and liquid in the digestion process (i.e., the quantity of VSdestroyed each day). As stated above, the SRT value represents the totalamount of conversion from volatile solids to biogas within the digestionprocess and therefore represents the overall efficiency of the digestionprocess in converting volatile solids to biogas. The equation belowdefines how SRT can be calculated:

${SRT} = \frac{(V)*({Cd})}{({Qw})*({Cw})}$V=Daily Infeed Volume into the Digester ProcessCd=Solids Concentration of the InfeedQw=Daily Quantity of VS destroyed, (COD infeed-COD discharge)where COD means chemical oxygen demand.Cw=Solids Concentration of the Waste Effluent (discharge from thedigester process)

Volatile Solids destroyed is related to the reduction in Chemical OxygenDemand. Initial destruction rates are relatively fast but, at some pointin the digestion process, the rate of VS destruction will dropdramatically, as indicated by a decrease in biogas production. At thatpoint, it is concluded that there will be limited benefit in retainingthe material with in the digester process any longer and therefore, thematerial is discharged. The total volatile solids destruction claimed istherefore based only on the destruction achieved while at the initialfaster rates. Therefore the Chemical Oxygen Demand of the thermophilicanaerobic digester 100 depicted in FIGS. 1 and 2 is equal to the netdifference in COD between the digester influent and effluent resultingfrom the volatile solids destruct rate over the period where thatvolatile solids destruct rate was fastest.

A measure of the success of biomass retention is the SRT/HRT (solidsretention time/hydraulic retention time) ratio. The thermophilicanaerobic digester 100 depicted in FIGS. 1 and 2 is adjustable in orderto achieve a SRT/HRT ratio that optimizes the volatile destruction andthe corresponding gas production. In some embodiments, the SRT/HRT ratioof the thermophilic anaerobic digester 100 depicted in FIGS. 1 and 2 isin excess of 1. A major influence is the much shorter HRT claimed by thesystem process. Current technology digesters have long HRT values. Thevolatile solids destruction in the generic systems is lower than in thethermophilic anaerobic digester 100 depicted in FIGS. 1 and 2 due to thenon-optimized mixing, heating and flow characteristics of material as itworks its way through the unit. In other technologies, where the SRT islow (fast) it does not allow enough time for the bacteria to grow andreplace the lost bacteria discharged with the digestate and if the rateof loss exceeds the rate of growth, “wash out” occurs. If this criticalSRT time period is breached, the digester performance falls offdramatically and substantial time is required to repopulate the bacteriaand restart the process.

In some embodiments, the thermophilic anaerobic digester 100 depicted inFIGS. 1 and 2 has a high SRT/HRT ratio while avoiding the washoutcondition. This unit can claim this process efficiency (high ratio) fortwo main reasons:

First: the thermophilic anaerobic digester 100 inoculates incoming freshfeedstock with a recirculated volume from the thermophilic anaerobicdigester 100 by transferring digestate from the end of the unit backinto upstream blend tank 102 through digester infeed valve 130 in theanaerobic digestion system depicted in FIG. 4. This is done upstream andbefore the new feedstock enters the thermophilic anaerobic digester 100.Without increasing the size of the digester 100, the exposure timebetween the bacteria and the feedstock has been extended. Thethermophilic anaerobic digester 100 achieves a larger effective HRTvalue by extending the exposure time of the feedstock to the inoculantsby use of blend tank 102 (upstream of the digester 100 itself). Thisintermixing of feedstock and bacteria occurs without increasing thedigester vessel volume and consequently, the HRT value is not increased.Maintaining a longer SRT and a higher SRT/HRT ratio avoids the potentialof a bacteria “washout” condition.

Second: the variable decanting capability at the discharge of thedigester enables the anaerobic digestion system 200 depicted in FIG. 4to draw the majority of the effluent from the middle valve 1388, wherethe solids resulting from incomplete digestion are of a lowerconcentration. The majority of the solids accumulate at the top andbottom of the digester 100, thus allowing the solids a longer residencetime inside the digester vessel 42. The net benefit is an effectivelylonger SRT without change to HRT and therefore a higher overall SRT/HRTratio. Variable decanting as detailed by the location of the middlevalve 138B FIG. 4 can be further extended. By mounting this valve at theouter edge of a commercially available sanitary flange connection at thedischarge end of the digester, the decanting of valve 138B elevation canbe adjusted by rotating the sanitary valve flange through 180° andthereby significantly adjusting the liquid level where the material isdrawn off. All sanitary fittings can be purchased industry wide, such asshown at www.jmesales.com/catalog/clamp-fittings sales brochures, whichare fully incorporated herein by reference.

A range of values can be used, but the real benefit is to have someadjustment as to where to draw off the digestate from the digester.Volatile solids destruction is somewhat asymptotic, with the first 65%of destruction happening quickly. The remaining 35% tends to flatten outwith smaller destruction rates over longer time periods. The anaerobesbreak down the organic matter into a liquid and the remaining ligninbased or inorganic material remain solid. To that end, the lighter solidmaterial (above valve 138B) should be removed from the digester at aslower rate at valve 138A to allow further destruction (because of moretime in the digester) or removal to avoid digester plug-ups. The heaviermaterial will be at a lower level than valve 138B and will need to beworked on longer. The material handled most quickly will be availablefor extraction at valve 1388. This weighted average approach to whichmaterials spend the longest time in the digester allows us to get aneffective volatile organic destruction end target without significantaddition to the hydraulic retention time (HRT).

The digester level valve that 138B services is easily adjusted, becauseit installed on a sanitary flange that can be rotated. The sanitaryflange is attached to the digester vessel

by a sanitary clamp which allows the rotation of the flange assemblythrough 180 degrees thereby raising or lowering the effective level ofvalve 138B based on the diameter of the flange and therefore on the endof the digester.

In some embodiments, the thermophilic anaerobic digester 100 depicted inFIGS. 1 and 2 avoids buildup of heavy organic and inorganic material atthe bottom of the vessel via self-cleaning and agitation. Once movedalong the inner circumference and to the top position, the material dueto its heavier weight will tend to migrate to the lower segments of theflow. Sloped orientation of the vessel in combination with the agitationgradually propels the heavier organic and inorganic matter to the end(discharge) of the digester 100. This feature enables the thermophilicanaerobic digester 100 to operate effectively with the presence ofinorganic matter and eliminating solids build up. This ensures avoidanceof digester component or sidewall premature wear, as well as theavoidance of periodic digester shutdown maintenance in order to clearinorganic buildups.

FIG. 3 depicts the structure of an example of a mechanical agitator 30used in the thermophilic anaerobic digester 100 shown in FIG. 1-2, wherecomponents 34, 36 and 38 of the agitator 30 are located 90 degrees aparton a radial basis to propel inorganic material along the bottom.Agitation is critical in that proper agitation works synergisticallywithin the thermal environment. The internal agitator arrangement runsthe full length of the digester 100 supported internally at the centerof the longitudinal axis of the mechanical agitator 30 and spans thefull diameter such that no region exists internally which is notagitated. One of the novelties of the agitator 30 is the flexibility tomodify the internal action of the agitator. The agitator 30 can beadjusted to be completely neutral, meaning that the agitation does notmove the plug flow along the length of the vessel 42 unless adjusted todo so. It can be modified to have a more directional sweep assisting inmoving heavier matter along the bottom of the digester 100. This is doneonly at the extreme radial end of the agitator near the inner wall. Thiswould not significantly disturb the plug flow integrity.

In some embodiments, each of the agitator components-agitator shaft 32,paddle frame structure 34, paddle plate 36, and localized end-of-paddlesweeps 38, and internal baffles 40—of the agitator 30 depicted in FIG.3, and FIG. 5(a)-(e) adopts an adjustable leading edge to cope withcontamination, such as the presence of sand in an agriculturalfeedstock. This inorganic and indigestible matter accumulates at thedecanting end of the digester 100 and is removed during the decantingprocess. The thermophilic anaerobic digester 100 has proven viable as aresult of continuous operations during the test period, withoutshutdowns due to sand build up. Upon shut down, the digester 100 wasemptied and the internals were inspected. Residual inorganic matter wasof diminutive volumes (of no consequence to the process) and was removedby simple manual labor and wash down.

In some embodiments, the agitator 30 depicted in FIG. 3 turns thematerial within the plug flow zone into itself by mixing radically awayfrom the central shaft of the agitator 30 out toward the outer vesselcircumference. Only rolling digestate movement is achieved with theagitator 30. This design mitigates problematic agitation (too violent).This gentle rolling agitation intimately brings nutrients to thebacteria and vice versa, which minimizes disturbance to the microbes andthus avoiding the condition where the anaerobes become dormant. Thisunique design feature ensures that the unit is self-cleaning and keepsthe feedstock solids from forming a crust at the top of the liquid levelwithin the digester. Any initial crust formation is re-submerged belowthe surface of the liquid within the digester and rewetted, therebyre-exposing it to the anaerobes.

In some embodiments, the length to diameter ratio geometry of 3:1 to 5:1of the vessel 42 permits the agitator 30 depicted in FIG. 3 to achieveoptimum thermophile and feedstock mixing without excess agitation, whichcould cause the anaerobes to go dormant. The internal agitatorconfiguration permitted by this vessel geometry achieves multipleobjectives. The agitation is gentle and neutral. The longitudinal vanesof components 34, 36 and 38 that run the length of the digester parallelto the vessel central axis of component 32 move the solids along thebottom and are assisted by the slope of the digester 100 and move solidsradially and axially based upon end of paddle sweeps 38. This has thecombined benefit of moving the nutrients to the anaerobes and thesettled heavy solid inorganic material (on digester bottom) to the endof the digester 100. This full diameter and longitudinal gentleagitation also keeps a crust from forming at the liquid interface, whichwould inhibit gas production and removal from the digester 100. Thesevanes continuously re-wet the lighter solids. This agitatorconfiguration also reintroduces some of the heavier organic material,which has tended to accumulate along the inside belly of the digesterback into intimate contact with the microbes.

In some embodiments, the agitator 30 depicted in FIG. 3 hasself-cleaning capability and is able to achieve complete, uniform butnon-violent homogenization of the vessel contents. In addition,temperature stratification and localized hot or cold spots areeliminated, thereby increasing digester efficiency. With the addition ofinternal baffles 40, biological integrity of the plug flow through thedigester is enhanced and maintained. These baffles, when combined withthe gentle agitation as described above, provide for a plug flowintegrity, such that the fresh feedstock progressively degrades intodigestate. These baffles also ensure the plug flow integrity of the paththrough the digester and avoid the mixing of material added mostlyrecently with that added earlier. No “short-circuiting” can occur.

Note that all agitator wearable parts and accessories (such as pumps,valves, etc.) are external and easy to replace or repair, should suchneed arises to external agitator bearings 46, ratchet and pawl agitatordrive 50 and agitator drive 144. Repairs are expeditious and only a fewhours downtime are required. The system is modular and thus the upset ofone digester is also not catastrophic.

FIG. 4 depicts an example of a process flow diagram of the anaerobicdigestion system 200 utilizing the thermophilic anaerobic digester 100shown in FIGS. 1 and 2. Primary components are numbered and defined onthe side of FIG. 4. Components of the system are a mix of commonindustrial components such as valves, field sensors, pumps and otherrelated process equipment which process unique equipment specific tothis novel invention. All components are required to allow thethermophilic process to operate successfully.

The anaerobic digestion system 200 depicted in FIG. 4 is operable at aslat barn dairy operation where the manure is pumped by chopper pumpfrom the barn pit to the blend tank 102. The blend tank 102 is designedand operated as a multifunctional device. The first function is toremove significant inorganic matter, such as sand, rock and relatedmaterials. The second function is to preheat the manure in preparationfor the subsequent process steps. The third function is to allowintroduction of exterior organic material (EOM) to the process. Theblend tank 102 has a conical bottom configured to remove inorganicmatter such as sand, pebbles and small rocks. The inorganic matter isthen discharged from the anaerobic process through inorganics 118. Onesignificance of the anaerobic digestion system 200 is the substantialremoval of inorganic material, with the remainder being removed byfurther measures discussed below.

The Feedstock

In some embodiments, a feedstock of known low nutritive value (aspertains to commonly held digester nutrients) can be used for thepurposes of prototypical testing of the anaerobic digestion system 200depicted in FIG. 4. The feedstock was dairy manure, sourced from theslat barn collection installation. The bedding initially was hay; butwas switched to wood shavings. The wood shavings, due to the lignincontent of the wood, do not digest readily. Thus, the wood shavingswould water log and accumulate along the bottom of the digester.Recognizing the fact that feed stock such as wood and related productsare not “digestible” with technologies such as claimed, verified is thefact that materials such as this presented no problem to the dailyoperation of the digester. In over continuous operation with this poorquality feedstock, the system proved capable of moving the sand, woodshavings and other settled material along the bottom of the digester fordecanting.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 operates with a multiplicity of feedstock materials. For the purposeof pilot testing, the worst case feed was chosen. This feedstockmanagement is crucial to achieving the anaerobic digestion systemoperating efficiency. The slat barn pilot test site was veryinefficient, and presented a worst case scenario for the anaerobicdigestion system 200 depicted in FIG. 4. This includes suchnon-controllable variables as: ground water dilution of the feedstock,inclusion of milk house wash down (with entrained antibiotics) andfluctuations in temperature, nutrient and inorganic parameters, as wellas feedstock consistency.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 digests organic matter. The system may not break down the lignin inwood products, but can handle lignin deleted material, if introduced inlimited quantities.

The slat barn collection process made impossible to collect fresh manureand transfer to the anaerobic digestion system. The anaerobic digestionsystem digests the volatile organic compounds (heretofore VolatileSolids or VS), which are normally >80% of the Total Solids (TS), asconfirmed by independent lab analysis. VS degrades with time, so freshmanure produces the optimum amount of biogas energy and higher digesterefficiency, as measured by solids destruction rates.

Decanted Digestate

Governing bodies and regulatory agencies worldwide recognize the benign(and even beneficial) environmental aspects of the anaerobic digestionsystem digestate. Therefore, regulations are much less stringent thanthose applied to the storage and disposal of untreated waste. In someembodiments, the anaerobic digestion system 200 depicted in FIG. 4discharges liquid digestate to the biomass tank 146 for processing andstorage. The digestate taken from the thermophilic anaerobic digester100 and transferred through discharge valve 138B can be analyzed throughlaboratory testing to confirm that there was no significant loss ofnutritional value (as represented by nitrogen, phosphorus and potassiumlevels here to fore NPK) incurred by the digestion process. Subsequentprocessing of the digestate yields separated solids which proved to be avaluable by-product as a soil amender and field testing with a localgreenhouse verified success. The by-product worked exceedingly well andsurpassed the greenhouse operator's expectations, as evidenced in singlesided testing. Significant increases in crop yield, quality and enhancedflavor were all observed and documented. Note that some sand mayaccumulate in the bottom of the bio mass tank 146, which requires anannual wash down. This minor maintenance is simple and has no effect onthe continuous operation of the anaerobic digestion system.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 stores digestate in one or more of: insulated equipment insulatinglayer 128, heated heat exchanger 106, blend tank 102, and bio mass tank146 during digester maintenance, allowing the slurry to remainbiologically active. This feature is key to allowing preventativemaintenance to be performed without significantly or deleteriouslyimpacting operational stability. Once system repairs are completed theslurry can be pumped back to the digester and the anaerobic digestionprocess immediately resumed.

The following is a detailed description outlining the attributes of thedesign of the anaerobic digestion system depicted in FIG. 4, includingthe upstream pre-treatment equipment and the digester vessel withdownstream capabilities.

Pre-Treatment

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 performs the upstream processes and activities via one or morecomponents of blend tank 102, process pump 104, heat exchanger 106,blend tank agitator 108, recirculation valve 112, digester feed valve114, consistency measurement sensor 116, inorganic valve 118, ph adjustchemical metering pump 120, blend tank discharge valve 122, temperaturesensor 124, temperature control valve 126, equipment insulating layer128 positioned throughout system 200, digestate infeed valve 130, blendtank level sensor 132 and ph sensor 136, wherein the upstream processesand activities are operational, chemical, biological and occurring priorto the in-feed of the main digester 100. As such, these components arean integral part of the anaerobic process. In addition to recirculatingin coming material for heating, chemical addition, and mixing forhomogeneity, this process pump 104 can also transfer prepared materialsto transfer into the digester 100. The various feedstocks are preparedfor digestion by processing the in-feed (raw) material as detailedbelow. These unit process steps are done at the blend tank 102 and theheat exchanger 106 located in the recirculation loop. The pre-treatmentsteps are accomplished and controlled within the blend tank 102. Rawmaterial is pumped into the tank 102 or conveyed in, depending on theconsistency of the feedstock. If the material is of a low consistency,it will be pumped directly into the tank 102. If it is of a higherconsistency, it will be conveyed or pumped into the tank 102 based uponthe site conditions. Adjustment of the carbon to nitrogen ratio may beperformed at this time through the addition of other feedstocks asdiscussed below. In the case of a feedstock with the optimal consistencyof 2% to 12%, the blend tank 102 and discharge process pump 104 willimmediately re-circulate the material through the heating loop and backinto the tank. In the event that steam is available as a heating sourceat the blend tank heat exchanger 106 and for the thermophilic anaerobicdigester 100, specifically for the digester heating system 170, a steampressure regulating valve 150 may be required.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 draws a specific volume of digestate (or that amount required fordilution) from the digester discharge and reintroduces/re-circulates itto the blend tank 102 to inoculate the new feedstock batch throughdigester discharge valve 138B and pumped via digester discharge pump 134back to the blend tank 102. This digestate is at the processingtemperature within the digester 100 so this will help to heat up thecontents of the blend tank 102. Off site inoculants may also be added asnecessary to increase the bacterial viability of the feedstock. Uponaddition of these inoculants, the level of agitation is decreased tominimize the “shock” effect on the thermophiles. In combination with theinoculation process, enzymes (which act as digestion catalysts) may beadded at this stage of the process. During the chemical addition, thelevel of agitation in the tank is increased to distribute the chemicalsquickly and uniformly by blend tank agitator 108.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 operates within a pH range of 4.0 to 8.5, however the optimal pH rangefor thermophiles is 7.5 to 8.0 and the optimal pH range for the incomingfeedstock is 6.5 to 7.0. Consequently, pre-treatment will have to adjust(if necessary) the pH parameters of the feedstock to within that pHrange by chemical injection using pH adjust chemical metering pump 120and pH sensor 136 located in the recirculation loop. For a non-limitingexample, the pH can be adjusted to >6.5. Conditions where pH is outsideof this range are tolerable but at dramatically reduced performancelevels. Performance is measured by reduction in Biological OxidationDemand (heretofore BOD), Chemical Oxygen Demand (heretofore COD) andproduction of Methane gas (heretofore CH₄). Methane is collected fromthe upper levels of the digester vessel 42 through the gas collectiondomes 48. Most methanogens are neutraphiles meaning that they performbetter in a pH range of 6.5 to 7.5. Thus by adjusting the pH to aminimum of 6.5 the feedstock is conditioned to a level of pH that isconducive to good methanogenic activity within the digester. With theaddition of internal baffles located along the length of the agitator,30 FIG. 3, the propelled feedstock through the digester length is atcertain key times forced to travel between the perimeter of the baffleand the internal diameter of the digester vessel 100 FIG. 2. Materialtesting for pH can be done at these specific locations with the additionof sample/chemical inject valve(s) on the outer sidewall of the digestervessel 100 FIG. 2. This in turn will permit the addition of pH adjustingchemicals in order to achieve/maintain a more anaerobic bacteria,supportive environment. The pH chemical addition pump 120 FIG. 4 can beused to inject the appropriate caustic or acidic chemistry to return thesystem to a more neutral pH condition.

As the addition of caustic or acid will be periodic the same chemicaldelivery system can be used as is required for the blend tank and usemanual sample—measurement—and injection into the digester at these“pinch points” or can automated later as the systems get larger.

Throughout this pre-treatment phase, blend tank agitator 108 mayaggressively blend and bring about homogeneity of feedstock particlesize within the blend tank 102. The blend is generally constructed ofcarbon steel and is insulated to retain process heat. Additionally, thespecifically configured conical section of the blend tank 102 combinedwith the tangential material flow located at the bottom of the blendtank 102 will remove large solid material greater than ⅝ inch indiameter. This step is required to reduce variations in oversize organicmaterial and optimize hydrolysis. Without doing so, the digesterperformance will be sub-optimal leading to reduced volatile solidsdestruction within the digester. In addition, this hydrolysis step mustbe completed to facilitate the downstream acidification step.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 preheats various feedstocks in the blend tank 102 to the processingtemperatures (such as within the thermal operating range of 9 rF to 158°F.) required for thermophilic digestion in the downstream digester 100using heat exchangers 106 and temperature sensors 124 located in theprimary recirculation loop. After the batch has reached the target pHlevel and required temperature, the system controls the recirculationvalve 112 and digester feed valves 114 to pump the contents to thedigester 100. If the feedstock is too low in temperature, it will shockthe thermophiles in the digester 100, thus negatively affecting theperformance of the anaerobic digestion system 200. The temperature ofthe feedstock must attain the operating temperature of the anaerobicdigestion system 200, which can range from 35° C. to 70° C. based uponthe anaerobic process selected. The thermophilic anaerobic digester 100will operate optimally

from 44° C. to 70° C.

During acidification stage following the hydrolysis, a new group ofbacteria called acetogens become active. These bacteria decompose aminoacids into acetic acid and hydrogen, nitrogen and carbon dioxide gases.To do this, they need oxygen, which they obtain from O2 dissolved in thefeedstock structure and liquid. While acetogens are anaerobic bacteria,oxygen is not as poisonous to them as to other anaerobes. The chemicalreaction that occurs when acetogens decompose amino acids is:2C3H7N03+02 2HC2H302+3H2+N2+2C02serine (amino acid)+oxygen acetic acid+hydrogen+nitrogen+carbon dioxide

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 performs and accomplishes much of this acidification stage upstream inthe blend tank 102 before injecting the feedstock into the digester 100.The feedstock is conditioned for pH and temperature and agitated topromote CO2 release prior to transfer to the digester 100. Note thatammonia can be toxic to the anaerobic digesting process. Ammonium,however, is far more benign and not toxic. Based upon independent andverifiable data, the blend tank 102 combines the ammonia with a free H(NH3+H NH₄+) and converts more than 95% of ammonia to ammonium which ismore environmentally benign and less odorous and is concurrent with thehydrolysis stage of anaerobic digestion. Ammonium locks in the nitrogen,preventing a rapid release into the soil, which will burn the plants.Lab results have shown that the effluent (digestate) is nearly free ofNH3 and the presence of NH₄+ is apparent.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 utilizes blend tank 102 and agitator 108 as a multi-functionalapparatus that expedites hydrolysis, acidification and ammonia toammonium conversion of the feedstock. It provides the means in which theCarbon to Nitrogen ratios can be adjusted as discussed below. It also

stabilizes the consistency of the feedstock and brings it to its desiredsolids percentage in the mixed slurry based upon the consistencymeasurement sensor within the blend tank recirculation loop.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 sets an optimal range of carbon to nitrogen ratio (C:N, which for anon-limiting example, can be a ratio of 20:1 to 25: during anaerobicdigestion. The microbes need nitrogen to multiply, therefore, if the C:Nratio is too high, microbial growth will be inhibited, which assumeslimited N₂ availability. On the other hand, if the C:N ratio is too low(i.e.—the carbon is too low), then the carbon supply for the methanogenswill be insufficient to sustain commercially viable methane production.The microbes combine the acetic acid made by acetogens with hydrogengas, and carbon dioxide to produce methane gas, water, and carbondioxide, according to the following equation:HC2H302+4H2+C02 2CH4+2H20+C02acetic acid+hydrogen gas+carbon dioxide→methane+water+carbon dioxide

Feedstocks come with a wide variety of C:N ratios. Therefore, thecritical need to adjust the C:N ratio in the blend tank 102, prior tothe digester in-feed, can be done by blending feedstocks. In the case ofa feedstock that is too low in carbon, it can be blended with anotherfeedstock high in nitrogen, to attain an optimal C:N ratio. Thispre-treatment practice is done at the blend tank 102 and the blendingfacilitates the chemical reactions.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 breaks down via blend tank 102 proteins by an enzyme called proteasethat is secreted by fermentative bacteria. This enzyme separatesproteins (polypeptides) into amino acids (peptides). It accomplishesthis de-polymerization through the hydrolysis process. In hydrolysis, awater molecule is inserted between the two amino acids that are bondedtogether. The blend bank 102 breaks the bond between them by capping thefree reactive ends with the H and the OH. The protein therefore, isbroken down from long chains into its individual molecules, amino acids.

In some embodiments, the blend tank 102 of the anaerobic digestionsystem 200 depicted in FIG. 4 inoculates the pre-treated feedstock withbacteria at the pre-treatment stage. Anaerobe rich digestate taken fromthe discharge of the digester infeed valve 130 can be used to inoculatenew incoming feedstock at the blend tank 102. The anaerobic digestionprocess is therefore, “seeded”. The amount of digestate required forbacterial inoculation will be independent from the amount of dilutionliquid required for the feedstock. Based upon monitored variables,including lab analysis, inoculation may also be accomplished withcommercially purchased materials. A booster of enzymes can also be addedduring this operational phase.

In some embodiments, the blend tank 102 of the anaerobic digestionsystem 200 depicted in FIG. 4 operates within a percent of totalincoming solids, for a non-limiting example, with a range of 0.5% to 20%(by weight). However, in the pre-treatment stage of the process thetargeted consistency at the blend tank 102/agitator 108 apparatus willbe 2% to 12% to facilitate easier handling and pumping. It is the dailyoperational decanting of the 3 decanting valves that allow the solids toaccumulate to a higher percentage in the digester. Various feedstockswill vary greatly as to their percent of dry solids. Some will have alow percentage of dry solids and thus can be pumped. Other feedstockwill have a high percentage of dry solids and therefore need to beconveyed. These solids percentage targets can be adjusted at the blendtank 102/agitator 108 pre-treatment stage. Conditions where percentincoming solids are outside of this range will result in detrimentalchanges in performance and output.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 removes large inorganic matter from the blend tank 102 via inorganicsvalve 118 during pretreatment. This operational activity occursprincipally at the blend tank 102/agitator 108 apparatus of thepre-treatment phase. Both organic and inorganic matter (such as sand,stones, bolts, screws, etc.) can be removed at this pre-treatment stage.However, the anaerobic digestion system 200 tolerates an acceptablerange of inorganic matter within the digester 100.

Digestion

Once the Pre-treatment process is completed, the inoculated feedstock istransferred to the thermophilic anaerobic digester 100 as depicted inFIGS. 1-2, where digestion takes place in a totally enclosed oxygen-freeenvironment, operating within a specific temperature range. Thefeedstock is conditioned to where the methanogen may be predominant. Thethermophilic anaerobic digester 100 can process organic waste within atemperature range of 35° C. to 70° C. to operate optimally. Outside ofdiscussed temperature ranges, the digester performance may be poor whenevaluated for volatile solids destruction, methane gas quality andquantity, pathogen reduction and quality of soil amendments.

In some embodiments, the water jacket on the underbelly of thethermophilic anaerobic digester 100 is generally comprised of two zonesfor temperature management of the digester 100. Such multi-zoneconfiguration heats the vessel contents along the entire digesterlength, maintaining constant and uniform feedstock/digestate internaltemperatures. Quantity of heat zones is based upon application and scaleof each usage environment. These zones can be controlled independently,sequentially or together. Two zones 170 are shown on FIG. 4 by way of anon-limiting example. The two heating zones are controlled byindependent digester zone one temperature sensor 158 and digester zonetwo temperature sensor 160, which correspondingly control temperaturecontrol valve zone one 152 and temperature control valve zone two 154.

In some embodiments, the thermophilic anaerobic digester 100 of theanaerobic digestion system 200 depicted in FIG. 4 utilizes threedecanting valves, top 138A, middle 138B, and bottom 138C, for variabledecanting in a digestate and capacity specific manner. The digester 100allows solids to build up at the top and bottom of the digester bydecanting from the middle valve. By selectively drawing digestate fromthe digester 100 at specific level(s), solids either above (lighter) orbelow (heavier) than the draw-off level are effectively exposed to thebacteria within the digester 100 for periods greater than the averageHRT of the vessels. Therefore, more complete digestion is achieved withcorresponding improvements in gas production, gas quality, and volatilesolids destruction. Solids build-up (both organic and inorganic) can bedecanted from the bottom and upper valves as needed. This in turn allowsfor channeling of various materials in the feedstock to differentoutflow streams. This ensures higher and more uniform product quality inthe high value product streams such as liquid and solid digestate. Therate of decanting at each of the valves can be adjusted individually tosuit the solids content and therefore adjust the SRT of that portion ofthe product stream.

Post Digestion

In some embodiments, the anaerobic digestion system depicted in FIG. 4operates as a batch plug flow system. With the addition of controls, thesize and frequency of loading the digester 100 can be adjusted such thatthe digestion process becomes almost continuous based on how it isoperated. The processing rate of the digester 100 is determined by theSolids Retention Time (SRT) requirements of the feedstock, which in turndefines the total volatile solids destruction and therefore, the biogasquality and the biogas quantity. In the case of manure, this alsodefines the percent conversion from ammonia to ammonium. Based onoptimizing the process parameters such as the in-feed plug flow volume,consistency, temperature, pH, digester operating temperature, decanting,and agitation can all be controlled by, for a non-limiting example, aprogrammable logic controller (PLC) system, which can also be used tomonitor methane and report methane quantity production levels. However,when necessary, there are manual over-rides that permit operation of theanaerobic digestion system in a manual mode.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 draws off biogas at the gas dome(s) of the digester 100 and piped to awater seal tank 180 to maintain an operating pressure within thedigester 100. This internal back pressure is adjustable by varying theliquid level in the water seal tank. This water seal tank 180 is also asafety device, in that it acts as an anti-flashback device or flamearrestor. Explosive or burning gases cannot get past the water seal andback into the digester vessel 42. The biogas bubbles up through thiswater bath and is subsequently cleaned through the removal of the fineparticulate entrained in the biogas. If a further reduction in thebiogas moisture content is required coalescing filters are used tocondense the entrained water vapor. The biogas flow is then measured forvolume and methane content. However, recognizing that various compoundsmay be collected due to the action of the water trap and may be of valuefor the utilization of the water trap is essential, considering the factthat the gas is of elevated temperatures adding of water manually may berequired.

In some embodiments, the anaerobic digestion system 200 depicted in FIG.4 further separates and processes the solids and liquids processed andstored in bio mass tank 146 via a solids liquid separator 148, dependingon the site conditions (water quality/BOD & COD requirements) and systemeconomics. A required level in the biomass tank 146 as identified bybiomass tank level sensor 140 can trigger the operation of the solidsliquid separator 148. The digestate that is transferred from thethermophilic anaerobic digester 100 is transferred by digester dischargepump 134 to the bio mass tank 146 through digestate valve 142 to biomass tank 146 which in turn is controlled by bio mass tank level sensor140. The process flow of the anaerobic digestion system 200 generatesdigestate that is highly suitable for land application as well as aproduct with a 99.999% pathogen kill. In addition, unlike otherprocesses, the digestion process is virtually complete and no furtheraerobic (wind-rowing) or secondary anaerobic digestion is required.Based upon marketing requirements of soil amendments, digestate needsonly to be further conditioned to achieve specific levels of moisturepercentage. A mechanical screw press; membrane; filters and reverseosmosis are methods for this purpose. Blending the initial organic wastestream with these other products to enhance the amount and value ofthese “byproducts” is referred to as co-digestion. The availability ofthese other “co-digestion” materials, adjacent and available to apotential anaerobic digester site requires that the overall process beflexible in handling a myriad of different “co-digestible” materials Asa non-limiting example, lignocellulose material is found in wheat straw,barley straw and most biomass. It is made up primarily of cellulose,hemicellulose and lignin. In addition, they are found in the woody stemsof vegetable and fruit waste generated at food processing plants. Ligninwithout pretreatment, such as microwave irradiation, significantlyimpedes the anaerobic digestion process by the anaerobes. These biomasssources as defined above represent a very large potential co-digestionmaterial source. Apart from incrementally adding co-digestion materialsto boost biogas volumes generated and enhanced soil amender or organicfertilizer properties, wheat and barley straw, and the like, are alsofound in the waste streams leaving dairy and other livestock barns. As anon-limiting example, spilt animal feed, partially digested wheat andbarley animal feed and stall bedding (straw) are also constituents ofthe waste streams leaving these concentrated animal feedlots. In oneembodiment microwave irradiation is applied to solubilize thislignocellulose material. As a non-limiting example this releases highlipid contents and transfers the nitrogen, potassium, and to a lesserextent phosphorous, from the solids faction to the liquid faction, andtransforms these high lignin materials into much in demand and readilyavailable co-digestion candidates. Given the relatively large amount ofsuch biomass, broad geographic availability, and the default disposal ofthis lignin through combustion or unconstrained off gassing via thecomposting process, biomass already present in these waste streamsrepresents reduced co-digestion acquisition costs as well as measurablyimproved byproduct production rates. Both improve anaerobic digesterpayback potential as applied to the food processing and agriculturalmarkets. By applying microwave, there is a disruption and break down ofcell wall membranes (“Lysis). In one embodiment, the target material tobe heated via microwave is the feedstock fed to the anaerobic digesterfor subsequent breakdown by the anaerobes while in the digester. Asnon-limiting examples, lysis and cell wall disruption are intended asinterchangeable. With regard to lignin, solubilizing the large andcomplicated multi-cell structures and converting to a liquid factionincorporates Lysis.

As a non-limiting example microwave, heats up the target material byinputting energy that in turn accelerates the vibration at the molecularlevel of the aqueous solutions associated with the organic feedstock.Target materials that represent good candidates for this type of energyinput should be aqueous. As a non-limiting example, an aqueous feedstockmust be material that can be pumped and therefore generally refers tomaterial that is 12 to 15% solids by weight or less.

In one embodiment the use of microwave to solubilize more of the TS(total solids) in the waste stream fed into the blend tank, illustratedin FIG. 4, more of the nutrients become available as soil amender andorganic fertilizer. Without this irradiation, the included lignin andits contained nutrients are inaccessible. As more of this nutrientmaterial, which as a non-limiting example can include nitrogen,potassium and phosphorous, moves into the liquid faction from the solidsfaction, the nutrient concentration of the digestate leaving thedigester is enhanced. This is also true for nitrogen and potassium. As anon-limiting example phosphorous requires additional pretreatment with acombination of microwave irradiation in a chemical (acidic) adjustedsolution. The blend tank process as defined illustrated in FIG. 4includes the process features to inject and adjust the pH of the blendtank using a chemical injection pump and sensing instrumentation,element 120 of FIG. 4, to automatically reach, maintain and repeat thismicrowave based solubilization. Any increased level of solubilizationwill improve access by the anaerobes in the anaerobic digestion phase togenerate more biogas, and improve the nutrient content of the digestatetea discharged at the end of the digester. As a non-limiting example,microwave for treatment of lignin in wheat straw or barley strawrequires at 120 kJ/liter, based on a retention time of 10 minutes and afinal temperature of 90° C. Similar values, ranging from 77 to 128kJ/liter are utilized to heat and treat dairy manure from an ambienttemperature, which as a non-limiting example can be at 20° C., up to85-95 with similar retention times. Limiting the temperature rise suchthat final temperatures are equal or less than 100° C. limitsvaporization of water that may be present. Excess vaporization increasesconsistency of the targeted material making recirculated pumpingunpredictable and increases the potential for formation of sludgecrusting on the inside sidewalls of the blend tank and more particularlyin the pipe cavity microwave, see FIG. 8, element 220, thereby reducingoverall performance.

As non-limiting examples microwave in its most recent configurations canbe designed and installed, such that thereby is input into the aqueousmaterial traveling through a pipe type cavity microwave unit. FIG. 6illustrates a cross sectional view F-F. As illustrated in FIG. 7, abypass flow line 205 is positioned around blend tank heat exchanger 106where the modular microwave pipe heater 210 would be inserted adjacentto heat exchanger 106.

As a non-limiting example this pipe type cavity microwave heater,illustrated in FIG. 8, is added to therecirculation/monitoring/homogenizing loop attached to the blend tank ofFIGS. 4 and 6. A magnetron wave generator within 210 uses wave guide 215to channel the microwaves into the pipe type cavity microwave 220, FIG.8. This configuration can include a radiation choke block element 225,FIG. 8, to provide errant microwave energy does not escape cavity 220.

As a non-limiting example the microwave frequency is adjustable tocompensate for the more limited penetration depth of microwave ascompared to radio frequency as well as the specifics of the biomasslignin targeted. This same feature permits power level adjustments toachieve the irradiation levels within the times required as well asachieve final treated material temperatures. This is illustrated in FIG.8 with choke dams 225, FIG. 8, to constrain microwave to the pipecavity-heating zone. As a non-limiting example the microwave radiationis applied to the most difficult constituents within the waste streamwhich can be the lignin based waste organics. Prior to the applicationof the blend tank chopper pump 104 to homogenize solids; incoming wasteorganics with lignin material have the largest particle size. Selectiveand sequential waste organic stream filtering prior to mixing at theblend tank concentrates lignin material into a smaller flow stream(volume) directed to the blend tank and the downstream anaerobicdigester.

In one embodiment the amount of lignin containing material that is addedto the blend tank and ultimately fed to the digester is constrained. Asa non-limiting example the application of microwave, as well as otherelectromagnet sources are suitable heating sources for the materialadded into the blend tank prior to injection into the thermophilicanaerobic digesters. In one embodiment the digester with electromagneticsource operates at temperature ranges between 44 to 70° C. and the needto use microwave to raise the targeted lignin containing materials is 90to 95° C. to achieve effective and beneficial solubilization. A thermalenergy balance is provided in order to limit lignin solubilizationvolumes in order to remain within the digester operating temperatureranges.

In one embodiment in order to achieve the retention times for effectivesolubilization, the volume of material to be treated by microwave in theparallel heating loop, as shown in FIG. 7 element 205 is controlled. Asa non-limiting example, larger particle size lignin material isselectively filtered upstream from the dairy barn flush flows or thewaste stream exiting the food processing plant. This material is fedfirst to the blend tank, as illustrated by element 102 in FIG. 4. Basedon the total solids content as received, it is diluted if required toachieve a 10 to 12% total solids content to permit recirculated pumpingthrough the microwave loop, element 205 of FIG. 7, bychopper/recirculating/transfer pump 104, FIGS. 4 and 7.

In one embodiment, other feedstock materials not requiring microwaveirradiation are then added to the blend tank for temperature, pH,percent solids and particle size conditioning as well as mixing with themicrowave treated materials. The overall particulate size distributionof the material leaving the digester (digestate) will however shift to asmaller micron (size) classification. The anaerobes because of improvedaccess to the volatile organic solids will generate more biogas but alsoreduce the percentage and size of remaining solids, which exit thedigester process. This in turn presents a further operational concerngiven the practical limitations in extracting very small micronparticulate from the digestate (digested material exiting the anaerobicdigester) flow when using lower cost filtration technologies andminimizing the dependency on high capital and operating cost optionssuch as centrifuges, as well as ultra-filtration and reverse osmosis.

in order to formulate the best fertilizing and soil amending attributesfor agricultural crop feeding, suspended soils with varying percentagesof nitrogen, phosphorous and potassium once filtered out of thedigestate flow are selectively added back into the “final digestate tea”to maximize nutrient value for the various specific crops and field soilconditions associated with each customer. This incentivizes the use ofthese recovered waters, organic based soil amenders and fertilizersthereby reducing the dependency on the use of chemical fertilizers andmaximizing byproduct value and demand.

As a non-limiting example microwave is only to those specific feedstockmaterials that benefit most from enhanced solubilization. Wastematerials fed to anaerobic digesters which can be accessed and processedmore quickly by the anaerobes can be heated with conventional steamheating. Other waste and/or co-digestion materials, which slow theoverall volatile organic solids destruction rates in the anaerobicdigester, including but not limited to lignin, are incrementally treatedby microwave to maximize lysis. This improves the anaerobe access andshortens hydraulic retention time. In one embodiment the materialsirradiated with microwave are those that yield the highest biogascontributions. This permits selecting which of these unit process stepsthat best enhances the system economics and payback.

In one embodiment selecting and processing these materials first in theblend tank with microwave requires consistent and controlled feedstockformulation. Over time, the variable decanting 138A, 138B and 138C inFIG. 4 can be used to evaluate which feedstocks have highest levels ofvolatile organic destruction rates as evidenced by the specificdensities of the materials at the end of the digestion process. Thisknowledge is then used to select the feedstocks that are the bestcandidates for microwave processing. As described previously equipmentis included in this process around the blend tank to homogenize andreduce feedstock particle size to improve access by the anaerobes to thefeedstock. This shortens the retention time (SRT, HRT) in the downstreamdigester(s). As a non-limiting example pump 104 is a chopper pumplocated in a heating and recirculation loop around the blend tank.Multiple passes through the heat exchanger 106 required to heat theblend tank contents also reduces and homogenizes feed stock particlesize. Pump 104 is also shown in the expanded sectional view of FIG. 7.The orientation of the sectional view F-F is defined in FIG. 6 andexpanded in FIG. 7.

In one embodiment, there are multiple process variable adjustments thatcan be made to achieve desired lignin solubilization. Pump 104 isequipped with a variable frequency drive such that pumping rates can beadjusted from 30% to 110% of fixed speed pump flow rates to effectivelyshorten or lengthen retention time within the microwave cavity for eachpumping cycle. The power input into the microwave pipe cavity can beadjusted at microwave 210 as illustrated in FIG. 7. The time allocatedfor preparation of this portion of the total batch of feedstock forsubsequent digestion can be adjusted to fine tune the amount ofmicrowave irradiation. When the other waste material is added to theblend tank, including but not limited to dairy manure with smallerentrained particle size, the overall heating can be accomplished byusing the microwave loop 210 in FIG. 7 or the steam heat exchanger loop106, as well as a blend of the two forms of heating.

In one embodiment the use of microwave with other heating sourcespermits exact final blend tank feed stock temperatures. Use of steamalone as used in the heat exchanger 106 can over shoot the final targettemperature given the latent heat remaining in the steam heatingjacket/heat exchanger at the blend tank. Microwave energy input isdiscreet. Once energy is removed from the microwave, further materialheating is stopped. As a non-limiting example, this can improve effortsto optimize feedstock delivery temperatures as well as more optimumanaerobic digester temperatures. Depending on the final temperature ofthe fluid when this occurs, dilution material can be added back to theblend tank after this “series of micro explosions” to return the aqueoussolution temperature back down to the mesophilic or thermophilicdigester operating temperatures if required.

Only after these events, would inoculants be added to this new batch offeedstock by way of digestate with entrained fragile anaerobes takenfrom the discharge end of the digester(s). This is possible given thehigh level of inline and real time process instrumentation installed atthe blend tank. Inline instrumentation coupled with PLC controlfacilitates the many different process sequences that can be programmedoptimized within blend tank process 102.

In one embodiment, solubilization can be further enhanced with the useof certain acids and or oxidizers, including but not limited to H2O2.This incremental step increases the solubilization of the nutrientphosphorous, which improves its transfer to the liquid faction, therebymaking it more available in the post digester “digestate tea” fororganic fertilizers and soil amenders. Given many dairy farms sufferfrom excess phosphorous accumulation, due to lagoon water application;avoiding the use of such chemistry binds more phosphorus in the solidfraction. In one embodiment post digester filtration removes solids highin phosphorous and allows the subsequent blending of digestate teas toachieve optimal and customizable nutrient constituents By adding backfiltered biosoids from the post digester discharge, higher valuedbyproducts can be generated. In one embodiment, other technologies canbe utilized to effectively rupture organic waste materials in an effortto release cell contents for easier anaerobe access.

Expected variations or differences in the results are contemplated inaccordance with the objects and practices of the anaerobic digestionsystem. It is intended, therefore, that the anaerobic digestion systembe defined by the scope of the claims which follow and that such claimsbe interpreted as broadly as is reasonable.

The invention claimed is:
 1. An anaerobic digestion system, comprising:a blend tank operable to control and perform pre-treatment of feedstock;an anaerobic digester operable to digest the feedstock provided from theblend tank in a totally enclosed oxygen-free environment within aspecific temperature range; a bio mass tank operable to process liquiddigestate from the anaerobic digester; one or more baffles positioned inthe digester, the one or more baffles providing for plug flow through atleast a portion of the digester and create baffled zones that are atleast partially operable independently of adjacent baffled zones; apaddle frame structure with a plurality of paddles, each of a paddlehaving an adjustable edge to cope with contamination; a first and asecond valve, at least one of the valves being mounted at an outer edgeof a flange connection at a discharge end of the digester to providevariable decanting capability at the discharge of the digester; and anenergy source coupled to the anaerobic digester.
 2. The system of claim1, wherein the energy source is an electromagnetic energy source.
 3. Thesystem of claim 1, wherein the energy source is a microwave source. 4.The system of claim 3, wherein the microwave source produces microwaveradiation that is applied to solubilize a lignocellulose material. 5.The system of claim 3 the application of the microwave radiationreleases high lipid contents.
 6. The system of claim 5, in response tothe release of high lipid contents there is a transfer of one or more ofnitrogen, potassium, and phosphorous from a solids faction to a liquidfaction.
 7. The system of claim 5, in response to the application of themicrowave radiation there is a transformation of high lignin materialsinto available co-digestion materials.
 8. The system of claim 3, inresponse to the application of the microwave radiation a disruption ofselected cell wall members is achieved “Lysis”.
 9. The system of claim3, wherein the microwave radiation is applied to a feedstock feed at theanaerobic digester.
 10. The system of claim 9, wherein the microwaveradiation is applied to a feedstock feed at the anaerobic digester forsubsequent breakdown by anaerobes while in the digester.
 11. The systemof claim 3, wherein the microwave radiation is applied to cause aheating of a target material that in turn accelerates a vibration at amolecular level of aqueous solutions associated with an organicfeedstock.
 12. The system of claim 3, wherein the microwave radiationprovides a solubilization of at least a portion of total solids in awaste stream fed into the blend tank.
 13. The system of claim 12,wherein the microwave radiation causes more nutrients to becomeavailable.
 14. The system of claim 12, wherein the microwave radiationis provided while limiting a temperature to the target material suchthat a vaporization of water present is limited.
 15. The system of claim12, further comprising: a bypass flow line positioned at least partiallyaround a blend tank heat exchanger.
 16. The system of claim 15, whereinthe bypass flow line is positioned at least partially around the blendtank heat exchanger where a microwave pipe heater is inserted adjacentto the heat exchanger.
 17. The system of claim 15, wherein a microwavefrequency is adjustable to compensate for a more limited penetrationdepth of microwave as compared to radio frequency.
 18. The system ofclaim 17, further comprising: choke dams to constrain microwave to apipe cavity-heating zone.
 19. The system of claim 3, wherein a volume oftarget material to be treated by microwave is controlled.
 20. The systemof claim 19, wherein larger particle size lignin material is selectivelyfiltered upstream from a dairy barn flush flow or a waste stream exitingfrom a food processing plant.
 21. The system of claim 3, whereinmicrowave radiation targeted materials are larger particle size ligninmaterial.
 22. The system of claim 21, wherein the microwave radiationtargeted materials are processed in the blend tank.
 23. The system ofclaim 3, wherein microwave radiation is utilized with a second heatingsource.